1. Field of the Invention
The present invention relates to a syringe which is composed of borosilicate glass and has a coating of the syringe cone for setting a defined surface roughness. Such a coating is applied in the form of a ceramic ink to the cone and baked. The ink composition used for this purpose consists of a glass frit, a roughness additive and liquid organic constituents which volatilize or decompose during baking. The glass frit melts and flows during baking, while the roughness additive does not melt during baking of the layer and essentially retains its shape and represents embedded, structure-forming particles in the molten glass layer which are raised on the surface of the layer. The glass matrix of the molten layer in which the structure-forming particles are embedded is also referred to as glass flux.
2. Description of Related Art
It is known that inorganic inks can be used for coating, also referred to as decoration or printing, of glass articles. Such inks contain one or more glass frits and optionally one or more color-coating components (pigments) in amounts of usually about 20% by weight. The glass frit is produced by melting and subsequent quenching and comminution of a glass composition. The glass frit obtained is milled to particle sizes of preferably less than 30 micrometers (μm) and mixed with the pigment powders.
Depending on the coating technique used, the powder constituents are mixed with specific organic suspension media, e.g. screen printing oil, to form a paste and applied to the glass substrate to be coated. The organic suspension medium has to burn out without leaving a residue before sintering and flowing and leveling of the glass powder because otherwise bubble formation occurs in the coating and the latter displays reduced adhesion to the substrate. The properties of the organic components play a part in determining the method of application, the reproducibility and the stability of the pastes in the application process. Critical parameters are the evaporation and drying behavior, the viscosity and the pasting ratio, i.e. the ratio of solid to liquid constituents or of organic component to inorganic powder. These parameters determine, inter alia, the layer thicknesses which can be achieved in the application process, when using the screen printing technique, the operating time of screens or of other printing elements and also the storage times of made-up inks in stock vessels.
In the baking process, the glass particles of the frit soften, flow and level out, envelop the color pigments and ensure, by means of diffusion processes, adhesion of the baked layer on the glass substrate. The glass particles of the frit are therefore essentially responsible for the chemical and physical properties of the decoration or ink layer after baking. The baking of the ink has to take place at below the deformation temperature of the glass substrate so as to avoid uncontrolled deformation of the substrate which has been printed, coated or decorated. For this reason, it is necessary to use low-melting glass frits which can be baked at below 700 degrees Celsius (° C.), especially for the decoration of, for example, borosilicate glasses having transformation temperatures of about 560° C.
The glass frits used hitherto for coating borosilicate glasses usually have a high lead content which is added in order to lower the baking temperature. Apart from the low baking temperatures, lead-containing glass frits have further technical advantages. They allow coating of borosilicate glasses having a low thermal expansion of from about 3 to 6·10−6/K without adhesion problems occurring. Furthermore, lead-containing glass frits make it possible to provide coatings having good chemical resistance towards acids and bases. This is an advantage for many applications of borosilicate glasses since these are frequently used because of their good chemical resistance.
Despite these good technical properties, the production and processing of lead containing glass frits is problematical, including during melting and milling. The toxic properties of lead-containing glass frits require special treatment in respect of handling, processing and disposal of the products decorated therewith. Due to new and stricter directives which limit the use of lead in glass frits, there is an increasing need for lead-free glass frits.
Commercially available lead-free inks for baking temperatures of about 650° C. have thermal expansions of greater than 6·10−6/K and therefore tend to be suitable for coating soda-lime glass having a thermal expansion of from about 8 to 9·10−6/K. The thermal expansion of such ink coatings is therefore not sufficiently matched to borosilicate glasses, and damage such as cracks, spalling and damage to the substrate glass can easily occur in the coated regions.
One possible way of reducing stresses between a coating and a borosilicate glass substrate is application of very thin layers, but this has the disadvantage of reduced color intensity. The chemical resistance of lead-free inks is also unsatisfactory for many applications.
The requirements which a coating of a cone of glass syringes has to meet are different from those for otherwise customary coatings for, for example, decorative purposes. To obtain color coatings having a good color intensity, layer thicknesses of greater than 20 μm are generally desired. The layer thickness of cone coatings, on the other hand, should ensure functionality and preferably be visible for the purposes of quality monitoring, but can be thinner. While conventional, decorative color coatings have to be smooth for aesthetic reasons and also to allow easier cleaning, the cone coating has to have a defined roughness. This defined roughness ensures that adapters placed on the cone of a syringe for the transfer of a liquid medicament present in the syringe cylinder stick firmly to the syringe or the cone thereof. These adapters are usually plastic adapters having a standardized geometry and having injection needles or tubing for the transport of the liquid attached thereto. The improved adhesion of the adapter to the cone associated with the defined roughness ensures that an adapter does not become detached by the internal pressure or lateral forces occurring during injection. A syringe adapter placed on the cone should also stick sufficiently well for it to remain firmly joined to the syringe body when pulling out the needle after injection. On the other hand, the roughness must not be too great because then there is the risk of an unsatisfactory seal. An unsatisfactory seal can lead to part of the medical liquid being expressed between adapter and syringe cone by the pressure required during injection and being lost, resulting in the surroundings being contaminated by the expressed droplets. Furthermore, prefilled readymade syringes containing medical liquid are sealed with closure caps on the cone after filling and stored. During this storage, a good seal is important so that the medical liquid is stored safely and sealed hermetically from the surroundings and atmosphere.
Pharmaceutical packaging is subject to more demanding requirements in respect of safety, toxic pollution and environmental friendliness. Thus, the EU directive EU 94/62/EC and also the packaging regulations Coneg applicable in the United States of America requires the total content of the elements Pb, Cd, Hg and CrVI to be limited to less than 100 parts per million (ppm) (corresponds to 0.01% by weight) per article. This limit value is easily exceeded when using cone coatings based on lead-containing glass frits, particularly in the case of small and light glass syringes.
Good adhesion of the coating without cracks, spalling of the coating and reductions in strength of the glass substrate occurring is therefore particularly important for the desired function of cone coatings. This requires matching of the thermal expansion of the cone coating to the type of glass of which the syringe is made. Stresses due to differences in the thermal expansion have to be minimized so that the abovementioned types of damage are avoided.
It is also desirable to have a good chemical resistance of the cone coating so that cleaning operations, e.g. autoclaving or washing of the glass syringe with usually acid or basic cleaning agents, do not attack the cone coating. The set roughness of the coating surface is also not intended to be altered by chemical attack.
To ensure that the glass body of a syringe composed of borosilicate glass does not deform during baking, the glass frit in the color also has to have a low baking temperature of less than 700° C.
Cone coatings for syringes are described in U.S. Pat. No. 4,589,871 A. The syringe bodies can consist of metal, plastic, glass and ceramic. Roughness additives described are powders of ceramic, glass, metal or combinations thereof to which an oil is added. This suspension is printed onto the syringe cone and the liquid constituents are partly vaporized in an oven, while the particles should remain adhering to the cone surface. However, no information is given for the cone coating of syringes of the borosilicate glass type with their low thermal expansion. There is also no information given as to the required nature of the roughness additive. Furthermore, it can be expected that the adhesion force of the applied particles to the cone leaves something to be desired. In addition, no roughness values are given for optimal functioning of the coating.
U.S. Pat. No. 5,851,201 A describes a syringe which is provided on the outside in the cone region with a textured surface for defined setting of the adhesion forces. The roughness is generated by embossing the texture into the surface of the syringe cone.
As an alternative to application of a coating having a defined roughness, the glass syringe can also be roughened in the cone region by means of grinding tools or sandblasting. However, it is difficult or complicated to provide a defined roughness in this way. In addition, these processes produce, especially in the case of syringes, very undesirable contamination due to abrasion and particles and make complicated cleaning steps necessary.